We propose to evaluate the efficacy of three screening tests - digital rectal examination, sigmoidoscopy, and fecal occult blood testing - in reducing mortality from colorectal cancer. All fatal cases of colorectal cancer in the Kaiser Permanente Medical Care Program from 1971-1987 will be identified from health plan cancer files. For each case, an age-, sex-and race-matched control who was till alive at the time of the case's death will be selected from membership files. Frequency of exposure to each screening test in cases and controls will be assessed by medical record review for the five or ten years before the case's diagnosis. Separate case-control analyses for each test will then compare exposure to that test among fetal cases which could have been detected by the test with exposure in controls. Exposure will be analyzed in terms of both number of each screening test during the five or ten years before diagnosis, and number of years since most recent exposure. Odds ratios for most recent exposure will be estimated by interval before diagnosis to assess duration of any protective effect. If a protective affect is noted, we will compare frequency of screening in advanced cases with that in a sample of early cases to establish that screening was indeed related to earlier detection. To evaluate possible confounders of an association of screening sigmoidoscopy and fatal colorectal cancer, we will examine computerized multiphasic health checkup records of a sample of 8,893 subscribers for whom a ten-year history of exposure to screening sigmoidoscopy is also available. We will compare persons having zero, one, and more than one screening examinations for characteristics that could confound case-control findings. Factors related to screening will be tested for association with risk of fatal colorectal cancer. If related to both, we will use the strength of these associations to adjust our case-control odds ratio estimates. Finally, the occurrence of colorectal cancer, both fatal and nonfatal, following negative sigmoidoscopic examinations will also be examined in these data. Using diagnosis of colorectal cancer during the two years after negative examination as the standard, we will estimate the false negative rate and sensitivity of sigmoidoscopy. This study, conducted in a setting where screening has bee relatively frequent and well-documented, would add significantly to the information available about the efficacy of these three screening tests.